A piezoelectric pump drive, especially for air pumps, in which a diaphragm is driven as a working member by a resonant oscillating system in an oscillating manner, is known from DE 10 2006 043 219 B3. This resonant oscillating system has at least one resonant spring, which is designed as a leaf spring, forms the oscillating arm and carries the resonant mass on a long lever arm. This long oscillating arm carrying the resonant mass is driven by a piezo element via a short driving lever in an oscillating manner, i.e., it is set to oscillate. The driving lever fixed stationarily with one end to a frame and the resonant spring are connected to one another in one piece, i.e., they together form one component. The oscillating means can be fixed in a defined plane in a simple manner due to the use of a leaf spring as a resonant spring, and leverages and hence motion transmissions between the driving lever and the resonant spring by which high work outputs can be attained with high efficiencies, are obtained due to the use of different lever arms of the short driving lever, on the one hand, and of the longer oscillating arm, on the other hand.
The resonant spring or oscillating arm is provided in various embodiments of this prior-art piezo drive at the end provided with the resonant mass with a rearwardly bent end section, which extends in parallel to the resonant spring and to which a so-called balance mass is fastened. This balance mass, fastened to the end section of the resonant spring, which said end section acts as a balance arm, brings about an at least approximately parallel oscillation of the end section or of the balance arm in relation to its extension, i.e., relative to itself. Whether this parallel oscillation is indeed achieved also depends, among other things, on the degree of bending elasticity of the balance arm and of the resonant spring. Since both the resonant spring and balance arm consist of a leaf spring in this prior-art piezoelectric pump drive, high bending elasticity can be assumed for both. However, high bending elasticity may lead to an oscillating characteristic deviating from parallelism.
The section of the resonant spring carrying the resonant mass or the resonant mass itself is connected directly to the working member of the working device, i.e., to the pump diaphragm of the fluid pump, via suitable coupling elements in this prior-art embodiment. The resonant mass fastened to the end section of the balance arm, which said end section is connected to the connection arc, and the coupling member connected thereto [said resonant mass—Tr.Ed.] do not perform any pure parallel oscillation in relation to the plane in which the valance arm extends, but an arc-shaped motion, which may have a harmful effect on the working member, i.e., on the pump diaphragm. Another embodiment of this prior-art piezoelectric pump drive is provided with a resonant spring, which has three spring legs, which are connected to one another in one piece by arc sections extending over 180° and are consequently directed rearwards and extend in parallel to one another in an S-shaped pattern. The resonant mass is arranged in the vicinity of the first arc section at the middle spring leg. The balance mass is located at the free end of the third spring leg. The coupling element, which connects this spring leg to the pump diaphragm, is also located approximately in the longitudinal center of this third spring leg. It can be assumed in this embodiment that the third spring leg oscillates in parallel to itself or to the plane in which it extends and that its motions do not have a harmful effect on the pump diaphragm.
However, a three-legged resonant spring is disadvantageous because it requires more space than an only two-legged spring and because it can get out of step more easily, i.e., it is more prone to trouble. In addition, it is more difficult to tune a three-legged spring to the adequate natural frequency than a two-legged one.
The resonant spring and balance spring consist of leaf springs each with high spring elasticity in this prior-art drive device, which experience has shown to be able to lead rather to resonance deviations and hence to operating troubles when a resisting force develops.